1. Field of the Invention
The present invention relates to oil level sensors, and more particularly to a capacitive oil level and temperature sensor for drive axle housings of motor vehicles.
2. Description of the Prior Art
Capacitive liquid level sensors are well known in the prior art. Typically, they use elongated capacitors immersed in the liquid, such as oil, and extended over the expected range of liquid level. These capacitors may be of various different types, such as concentric cylindrical tubes or spaced plates. It is generally known to use capacitive liquid level sensors in motor vehicles for measuring an oil level in an engine and transmission. However, capacitive sensors currently used in the motor vehicles, are not readily adaptable for measuring oil level in a drive axle housing, especially in the rigid drive axles of trucks, due to clearance limitations within the drive axle housing and few openings through which to apply the sensor. Thus, there is a need for a capacitive liquid level sensor specifically adapted to be mounted in the drive axle housing of the motor vehicles.
The present invention provides a motor vehicle drive axle housing including a capacitive liquid level sensor specifically adapted to be mounted in an drive axle housing of a motor vehicle. Normally, the drive axle housing includes an oil reservoir containing a predetermined amount of oil adapted to lubricate axle gearing and bearing assemblies. The capacitive oil level sensor in accordance with the present invention comprises an L-shaped hollow body allowing for a simple fit in current production drive axles. The L-shaped hollow body of the oil level sensor comprises a pair of mutually perpendicular legs. A substantially vertically oriented first leg includes an oil level detecting capacitor and adapted to be at least partially immersed in the oil reservoir. The oil level in the oil reservoir is determined as a function of electric capacitance of the sensor capacitor. The oil level sensor in accordance with the present invention may include a thermistor for measuring a temperature of the oil, also disposed in the sensor body. A second leg is substantially horizontally extending from the drive axle housing and contains an electronic sensor circuitry electrically coupled to the oil level detecting capacitor and the thermistor, and adapted to generate oil level and temperature output signals. Preferably, the electronic sensor circuitry includes a digital microcontroller. The electronic sensor circuitry may include a radio frequency (RF) transmitter to wirelessly transmit the oil level and temperature output signals.
Furthermore, the second leg of the sensor body is provided with a cylindrical, threaded mounting surface suitable for screwing the sensor into a threaded opening in the drive axle housing in order to lock and orient the sensor in its place, and a nut member facilitating the installation of the oil level sensor.